1. Field of the Invention
The present invention relates to an exposure device used in the manufacturing of semiconductor devices. More particularly, the present invention relates to an air shower head for producing a shower of air that envelops a wafer during a semiconductor device manufacturing process of exposing photosensitive material on the wafer.
2. Description of the Related Art
Impurities are precisely regulated and are injected into small regions of a silicon substrate to manufacture a fine circuit. Such regions are mutually connected to form a device and a VLSI circuit. A pattern formed by photolithography is used to define the regions. That is, a wafer is coated with a photosensitive resist (photoresist layer), the photoresist layer is irradiated with light (ultraviolet light) projected through a photomask bearing a pattern to thereby expose selected portions of the photoresist layer, and the photoresist layer is then developed. The developing of the photoresist comprises removing the exposed or unexposed portions thereof to produce a photoresist pattern having a form identical to or opposite to that of the pattern of the photomask.
The photoresist protects the substrate in the process of forming a semiconductor device or semiconductor chip. In addition, the substrate is processed, e.g., by chemical and physical deposition and plasma etching, using the photoresist pattern as a mask.
An example of a device for performing the above-described photolithography process is disclosed in U.S. Pat. No. 5,963,324.
The technology of photolithography has been regarded as one of the essential technologies in the manufacturing of semiconductor devices. Recently, high degrees of integration characterized by design rules of less than 0.25 microns have been achieved in semiconductor devices. The processes of manufacturing semiconductor devices must, therefore, have characteristics suitable for accomplishing such high degrees of integration.
However, among the characteristics of semiconductor manufacturing processes, air quality, i.e., contamination in the environment in which the processes are carried out, has been a problem. In particular, in photolithography, a chemical such as ammonia or amine reacts with the compound of the resist that is to be activated by the ultraviolet light and thereby prevents such a reaction from taking place, that is, prevents the resist from being exposed during photolithography. A method of passing air through a chemical filter, producing a shower of the air in the vicinity of a lens of the photolithography equipment, and directing the air towards the wafer has been suggested as a means for preventing such chemicals from contaminating the wafer (see Japanese Patent Laid-Open Pub. No. Hei 9-283401).
More specifically, an air shower head is provided in the vicinity of a lens of the exposure device. Clean air is supplied by the air shower head around the wafer to prevent the wafer from being contaminated.
FIG. 1 shows a prior art air circulation system for supplying air into an exposure device. Referring to FIG. 1, cooling water is supplied to one side of an air conditioning device 10 through a cooling water line 12. Air, on the other hand, is supplied to the other side of the air conditioning device 10 through an air circulation line 50. The air supplied to the air conditioning device 10 through the air circulation line 50 undergoes a heat exchange with the cooling water, and is then supplied to a filtering device 20. Chemicals are filtered out of the air by the filtering device 20. The filtered air is then supplied to an air distributing device 30 comprising first, second, and third air supplying lines 50a, 50b, and 50c. 
Some of the air is supplied to the exposure device (not shown) via the first supplying line 50a of the air distributing device 30. The air traveling through the second supplying line 50b passes through a first filter 32 in which particulates in the air are filtered, and then is supplied to a wafer orienting stage or a wafer feeding system. The remainder of the air travels through the third supplying line 50c and from there passes through a heat exchanger 36 and a second filter 34, whereby the temperature of the humidity of the air are regulated. This portion of the air is supplied to an air shower head disposed above a wafer stage of the exposure device.
Referring to FIGS. 2 and 3, the air shower head 100 is disposed under a lens system 140 of the exposure device. More specifically, the air shower head 100 is interposed between a wafer (not shown) and the lens system 140 of the exposure device. The air shower head 100 comprises an upper frame 120 and a porous member bottom 130 attached to the bottom of the upper frame 120.
The upper frame 120 has an upper wall 126, an inner side wall 124 and an outer side wall 128. The inner side wall 124 defines a concavity in the top of the shower head 100, and the upper side wall 126 defines a flat (horizontal) surface at the periphery of the concavity. The air shower head 100 also has a hole 122 extending through the center of both the upper frame 120 and porous member 130 and by which light transmitted through the lens system 140 can propagate to the wafer. The inner side wall 124 together with the porous member 130 form a tapered portion of the air shower head 100 at an intermediate portion thereof as taken in the radial direction. That is, the thickness of the air shower head 100 increases radially outwardly from the hole 122 to the flat surface defined by the upper wall 126. The shower head 100 is hollow, i.e., a space therein is delimited by the porous member 130 and the upper wall 126 and side walls 124,128 of the frame 120.
Referring now to FIGS. 3 and 4, the bottom end 128a of the side wall 128 of the upper frame 120 is bonded to the porous member 130. Similarly, the bottom end 122a of the side wall 124 is bonded at the penphery of the hole 122a to the porous member 130.
The porous member 130 is made of a woven fabric comprising chemical resistant yarn. The yarn is woven in the form of a matrix leaving a plurality of fine holes between individual ones of the yarns. FIG. 4 shows the state in which the bottom end 122a of the side wall 124 of the frame 120 is bonded to the porous member 130 at the periphery of the central hole of the shower head. Specifically, the porous member 130 is attached to the frame 120 using a chemical binder 110.
The third air supplying line 50c shown in FIG. 1 is connected to one side of the air shower head 100 so that air is supplied into the air shower head 100. The air is injected through the fine holes of the porous member 130 towards the upper surface of the wafer. Thus, a higher pressure is created in the region of the wafer stage than in the surrounding region. As a result, foreign matter is prevented from being introduced onto the wafer from the surrounding region.
However, the air shower head produces organic contaminants during the manufacturing (photolithography) process. Specifically, organic contaminants are continuously produced in the form of a gas from the binder which is used to bond the upper frame 120 to the porous member 130. Furthermore, the yarn of the porous member is engaged with the upper frame of the air shower head. Thus, the yarn separates into particles or fibers which adhere to the wafer and thereby contaminate the photoresist film.
The present inventors have confirmed, as follows, that the air shower head of the prior art is a source of contamination for a wafer undergoing photolithography. Using the air supply system of FIG. 1, air supplied to a wafer stage of an exposure device through the third air supplying line 50c and the prior art air shower head was retrieved and supplied to a first bare wafer. Air supplied to a wafer feeding system through the second air supplying line 50b, i.e., without passing through an air shower head, was retrieved and supplied to a second bare wafer.
The bare wafers were cleaned, using a fluoride solution and a standard cleaning solution, before the air was supplied thereto. The respective portions of air were supplied to the bare wafers for four hours. FTIR by the wafers were measured to analyze the organic substances which were present on the wafers. FIG. 5 shows the presence on the first and second bare wafers of organic substances having Cxe2x80x94H bonds, whereas FIG. 6 shows the presence on the first and second wafers of organic substances having Cxe2x80x94X (wherein X is a halogen), Sxe2x95x90O, Cxe2x80x94N bonds.
In FIGS. 5 and 6, the dotted lines represent a measure of contaminants on the first bare wafer, and the solid lines represent a measure of contaminants on the second bare wafer. Accordingly, FIGS. 5 and 6 clearly prove that the air retrieved from the wafer feeding system is less contaminated than the air retrieved from the wafer stage after having passed through the prior art shower head. Examples of the organic substances, that is the contaminants, are 1-buthanol, 3-methyl 1-heptene, 4-methyl 1,6-dioxasiclorodekan-7, 12-dion2-heptene, 3-methyl 2-penthanol, 2-penthanon, 4-methyl 2-propanol, 1-metoxy propion acid, trimethyl-2,4,4 hexane-1 and chlorine. These contaminants corrode the equipment, and produce haze on the surface of the lens, thereby lowering the intensity of the light transmitted therethrough onto the photoresist film. Furthermore, the organic substances react with the photo-activatable compounds of the photoresist film and inhibit the forming of patterns thereon by the light, i.e., render the compounds inactive.
An object of the present invention is to solve the above-described problem of the prior art by providing an air shower which will not serve as a source of contamination and will not act to degrade the profile of a wafer that has undergone photolithography while showered with air by the air shower head.
In order to achieve the above-mentioned object, the present invention provides an air shower head of photolithography equipment, in which the porous bottom member is mechanically clamped to the upper frame instead of being chemically bound thereto.
Specifically, the inner and outer circumferential side walls of the upper frame each have U-shaped portions at the bottom ends thereof. The inner and outer circumferential ends of the porous bottom member extend into the U-shaped portions, respectively, and are crimped thereby.
Alternatively, discrete clamps secure the inner and outer circumferential ends of the porous bottom member to peripheral portions of the bottom ends of the inner and outer circumferential side walls of the upper frame.
According to the present invention, because the air shower head does not comprise a chemical binder, the photoresist film on the wafer will not be contaminated by organic materials which can render the photo-activatable compound thereof inactive, and the lens will not become hazy due to organic substances. Accordingly, a high quality photoresist pattern can be produced when the air shower head of the present invention is employed.